1. Field of the Invention
The present invention relates to an improvement in a multiplate clutch outer part which is formed by pressing a steel plate and which comprises: an end wall portion; and a cylindrical portion having its one end formed continuously with an outer peripheral end of the end wall portion, and opened at the other end, the cylindrical portion including: a large number of spline grooves and spline projections which are formed in an inner peripheral face of the cylindrical portion, and which extend in an axial direction, the spline grooves and the spline projections being alternately arranged in a circumferential direction of the cylindrical portion; and outer projections and outer grooves which are formed in an outer peripheral face of the cylindrical portion, and which are arranged in positions corresponding respectively to those of the spline grooves and the spline projections.
2. Description of the Related Art
Such a multiplate clutch outer part is known, for example, as disclosed in Japanese Patent Application Laid-Open No. 3-288018.
In press working for forming such a multiplate clutch outer part, drawing for forming the cylindrical portion and ironing for forming the grooves and projections on the inner and outer peripheral faces of the cylindrical portion are simultaneously performed in parallel. In particular, the ironing resistance is increased, as the diameter of the cylindrical portion is smaller and the cylindrical portion is longer; and also increased with the progress of forming. If the ironing resistance is excessively increased, a forming defect such as crack or breakage occurs in the vicinity of the boundary between the end wall portion and the cylindrical portion.